A comparison of the Universal Time and local latitude deduced from the Astrolabe observations since 1966 to 1970, with respect to similar results obtained from BIH datas, show significative annual differences, specially in time, of a stable pattern. The consistence of the latitude differences (Astrolabe – BIH) and latitude group corrections, computed by the chain method, prove that these differences could be explained by the influence of a systematic error in the FK4 of Δδα type. On the other hand the inconsistence of the strong annual differences in time with the time group corrections, show that these differences can not be explained by catalogue systematic errors. The group corrections in time are compared with an investigation of the FK4 Δαα error based in the observations made with a transit instrument at Santiago.